The present invention relates to liquid spraying apparatus in general, and more particularly to improvements in apparatus for atomizing one or more liquid streams and for applying the atomized liquid to a moving body, particularly to a running web or tow of filamentary material which is about to be converted into the filler of a filter rod. Still more particularly, the invention relates to improvements in apparatus which can be utilized with advantage for atomization of a plasticizer, such as triacetin, and for the application of atomized plasticizer to a tow consisting of acetate fibers or like filamentary material which is capable of intercepting substantial percentages of deleterious ingredients of tobacco smoke.
It is already known to equip a filter rod making machine with an apparatus which applies atomized plasticizer to a running web or tow of filamentary filter material. Such a machine normally comprises two sections or units, namely, a first or tow processing unit wherein a tow of filamentary filter material which is drawn from a bale is spread out to form a thin layer so that all or nearly all of the filaments are exposed for uniform application of an atomized plasticizer (particularly triacetin), and a second unit or section wherein the thus treated tow is converted into a rod-like filler and is draped into a web of cigarette paper or other suitable wrapping material to form therewith a continuous filter rod which is thereupon subdivided into filter rod sections of desired length. The means for applying atomized plasticizer to the spread-out tow in the first unit of such a machine includes one or more rotary brushes and means for supplying metered quantities of plasticizer to the brushes. The brushes convert one or more streams of like bodies of liquid plasticizer into fine droplets which are sprayed onto the running tow so that the plasticizer contacts all or nearly all filaments and enables the filaments to form a myriad of intricate paths for the flow of tobacco smoke toward the mouth of the smoker. The quality of filter plugs which are obtained from the aforementioned filter rod depends, to a considerable extent, on the degree of uniformity with which the filaments of the tow are contacted by atomized plasticizer. The degree of uniformity, in turn, depends on several factors such as proper spreading and tensioning of filaments which form the tow, the selected rate of delivery of plasticizer to the atomizing instrumentality or instrumentalities, and the nature of atomizing action.
In addition to brushes, it is also known to employ atomizing devices in the form of impeller wheels and nozzles. As of late, rotary brushes constitute the preferred atomizing devices because their bristles can readily break up a continuous stream or pool of liquid plasticizer into minute droplets. In most instances, the bristles of a rotating brush sweep along a surface which is coated with a film of liquid plasticizer whereby the bristles undergo deformation and thereupon recoil to propel minute droplets of plasticizer against the running filamentary filter material. A drawback of such atomizing apparatus is that the bristles of the brushes undergo rapid and often non-uniform wear so that the brushes must be inspected and replaced at frequent intervals. In the absence of replacement of a brush whose bristles have undergone pronounced wear, the bristles are likely to furnish a gradually deteriorating atomizing action so that the apparatus begins to propel large droplets of non-atomized plasticizer against the adjacent portions of the travelling tow. Apparatus which employ one or more brushes for atomization of plasticizer are disclosed, for example, in commonly owned U.S. Pat. Nos. 4,132,189 to Greve et al. and 3,974,007 to Greve.